1. Field of the Invention
The present invention relates to a lithographic apparatus, a thermal conditioning system, and a method for manufacturing a device.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
In lithographic apparatuses, a projection system is provided for projecting the pattern onto the target portion on the substrate. Typically, the projection system includes a lens which is mounted on a reference frame. The reference frame provides multiple functionalities and requires a highly stable environment. The reference frame may also be referred to the metrology (or metro) frame in the art. In conventional lithographic apparatuses, the projection lens is mounted on the reference frame using lens support blocks. The projection lens, lens support blocks and reference frame form part of a stability chain. It has been found that as the imaging accuracy requirements of lithographic apparatuses increases the thermal stability of the projection lens, lens support blocks and reference frame is desired to be improved. Otherwise a drift in the reference frame is found to occur, which is highly undesirable. Further, it has been found that the accuracy of measuring apparatuses within the lithographic apparatus, in particular, interferometers, which are also mounted on the reference frame, is affected by a drift in the reference frame. A further problem is that the thermal conditioning of the projection lens is compromised.